RECORD: Darwin, C. R. 1868. On the character and hybrid-like nature of the offspring from the illegitimate unions of dimorphic and trimorphic plants. [Read 20 February] Journal of the Linnean Society of London (Botany) 10: 393-437.

On the Character and Hybrid-like Nature of the Offspring from the
Illegitimate Unions of Dimorphic and Trimorphic Plants. By CHARLES
DARWIN, M.A., F.R.S., F.L.S., &c.1

[Read Feb. 20, 1868.]

TABLE OF CONTENTS.

Preliminary
explanation.

Primula Auricula,
equal-styled var. of.

Lythrum Salicaria,
various illegitimate unions and character of offspring.

Primula vulgaris,
transmission of form and fertility of illegitimate offspring.

Concluding remarks on Lythrum.

Primula veris,
transmission of form and fertility of illegitimate offspring.

Oxalis rosea,
transmission of form.

Equal-styled red variety of P.
veris.

Primula sinensis.

Pulmonaria,
transmission of form.

Summary on the transmission of
form, constitution, and fertility of the illegitimate offspring of P.sinensis.

Conclusions in regard to the
illegitimate offspring of trimorphic and dimorphic plants.

Equal-styled variety of P.
sinensis.

VARIOUS plants, which I have called dimorphic and
trimorphic, have been described by me in papers read before this
Society*. But it may be convenient to recall as briefly as possible the
meaning of these terms. Dimorphic species consist of two forms, which
naturally exist in about equal numbers: in the long-styled form the
pistil is always longer, and the stamens (excepting in the case of Linum
grandiflorum)are shorter than in the other form.
Conversely, in the short-styled form the pistil is shorter and the
stamens longer than in the long-styled form. In the latter the
pollen-grains are almost always of larger size than in the short-styled
form. The sexual union of the two distinct forms is necessary for full
fertility: such unions I formerly called heteromorphic; but, for
reasons which will immediately appear, it is more convenient to speak
of them as legitimate, and the offspring thus produced, as ordinarily
occurs in nature, as legitimate. When long-styled or short-styled
plants are impregnated with their own-form pollen, the union is not
fully fertile, or is even absolutely barren. Such unions, and the
offspring raised from them, may be called illegitimate. Thus two
legitimate and two illegitimate unions can be effected.

With trimorphic species, the case is more complex.
There are three forms, which differ greatly in the length of the
pistil; and in each form two sets of stamens exist, differing in
length, in the

size of the pollen-grains, and often in colour. The
stamens are graduated in length, so that one of the two sets in two of
the forms is equal in length to the pistil in the third form. For
instance, in the long-styled form the pistil equals in length the
longer set of stamens in the mid-styled and short-styled forms. In all
three forms the union is fully fertile and legitimate only when the
pistil is impregnated with pollen from the stamens which equal it in
length. Thus the long-styled form can be legitimately fertilized only
by the longer stamens of the mid-styled or short-styled form; it can be
illegitimately fertilized by its own two sets of stamens, and by the
shorter stamens of both the mid-styled and short-styled forms; so that
the long-styled form can be fertilized legitimately in two ways and
illegitimately in four ways. The same holds good with the mid-styled
and short-styled forms; hence with trimorphic species eighteen unions
are possible, of which six are legitimate, and produce legitimate
offspring, and twelve are illegitimate and produce illegitimate
offspring.

I will give the results of my experiments on the
illegitimate offspring of various dimorphic and trimorphic plants in
full detail, partly because the observations are extremely troublesome,
and will not probably soon be repeated (thus I have been compelled to
count under the microscope above 20,000 seeds of Lythrum Salicaria),
but chiefly because much light is thus indirectly thrown on the
important subject of hybridism.

LYTHRUM SALICARIA.

I will commence with this trimorphic species. Of the
twelve illegitimate unions, two were completely barren; and I succeeded
in raising seedlings from only six, or doubtfully from seven, of the
remaining ten illegitimate unions. The experiments are arranged in
classes according to the parentage of the plants. In each case I give
the average number of seeds per capsule, generally taken from ten
capsules, which, according to my experience, is a nearly sufficient
number. I give also in each case the maximum number of seeds in any one
capsule; and this is a useful point of comparison with the normal
standard—that is, with the number of seeds produced by legitimate
plants when legitimately fertilized. I give likewise in each case the
minimum number. When the maximum and minimum differ greatly, and no
remark is made on the subject, it may be understood that the extremes
are so closely connected by intermediate figures that the average is
fair. Large

capsules were always selected for counting, in order to
avoid overestimating the infertility of the several illegitimate
plants. The plants were generally allowed to be freely and legitimately
fertilized, through the agency of bees, by illegitimate plants
belonging to the two other forms growing close by. This is
the fairest plan, and was generally followed; but in several cases
(which will always be stated) illegitimate plants were fertilized by
pollen taken from legitimate plants belonging to the other two forms;
and this, as might have been expected, increased their fertility.
Unfortunately
Lythrum Salicaria is much affected in its fertility by the
nature of the season; and to avoid, as far as possible, error from this
source, my observations were extended over several years. Some few
experiments were tried in 1863. The summer of 1864 was too hot and dry,
and, though the plants were copiously watered, some few apparently
suffered in their fertility, whilst others were not in the least
affected. The years 1865 and, especially, 1866, were highly favourable.
Only a few observations were made during 1867.

In order to judge of the degree of infertility of the
various illegitimate plants, the following statement of the average and
maximum number of seeds produced by ordinary or legitimate plants, when
legitimately fertilized, some artificially and some naturally, will
serve as a standard of comparison, and may in each case be referred to.
But in order to save trouble, I have given under each experiment the
percentage of seeds to the nearest whole number, as calculated in
comparison with the standard number of the same form.

Standards.

Long-styled form; average number of seeds in each
capsule 93; maximum number observed in twenty-three capsules,
159.

Mid-styled form; average number of seeds, 130;
maximum number observed in thirty-one capsules, 151.

Short-styled form; average number of seeds,
83.5; but we may, for the sake of brevity, say 83; maximum
number observed in twenty-five capsules, 112.

CLASS I. Illegitimate plants from the long-styled
form, fertilized by pollen from the longer or shorter stamens
of the
same form.

From this union I raised at different times three lots
of seedlings, amounting altogether to 56 plants. I must premise that,
from not foreseeing the result, I did not keep a memorandum whether the
eight plants of the first lot were the product of the

longer or shorter stamens of the same form; but I have
reason to suspect that they were the product of the latter. These eight
plants were much more dwarfed, and much more sterile than those in the
other two lots. The latter were raised from a long-styled plant growing
quite isolated and fertilized by the agency of bees with its own
pollen; and it is almost certain, from the relative position of the
organs of fructification, that the stigma under these circumstances
would be fertilized by pollen from the longer stamens.

All the fifty-six plants in these three lots proved
long-styled; now, if the parent plants had been legitimately fertilized
by pollen from the longer stamens of the mid-styled or short-styled
forms, about one-third alone of the seedlings would have been
long-styled, and the other two-thirds would have been mid-styled and
short-styled. In some other trimorphic and dimorphic genera we shall
find the same curious and inexplicable fact, namely that the
long-styled form, fertilized by its own-form pollen, produces almost
exclusively long-styled seedlings*.

The eight plants of the first lot were of low stature:
three which I measured attained, when fully grown, the heights of only
28, 29, and 47 inches; whilst a legitimate plant growing close by
reached the height of 77 inches. They all betrayed in their general
appearance a weak constitution; they flowered rather later in the
season, and at a later age than ordinary plants. Some did not flower
every year; and one plant, in an unprecedented manner, did not flower
until three years old. In the two other lots none of the plants grew
quite to their full and proper height, as could at once be seen by
comparing them with the adjoining rows of legitimate plants. In several
plants in all three lots, many of the anthers were either shrivelled or
contained brown and tough, or pulpy matter, without any good
pollen-grains, and they never shed their contents; they were in the
state designated by Gärtner† as contabescent, which term I will for the
future use. In one flower all the anthers were contabescent excepting
two, which appeared to the naked eye sound; but under the microscope
about two-thirds of the pollen-grains were seen to be small and
shrivelled. In another plant, in which all the anthers appeared sound,
many of the pollen-grains were shrivelled

* Dr. Hildebrand first called attention
(Bot. Zeitung, Jan. 1, 1864, S. 5) to this subject in the case of Primula
sinensis; but his results were not nearly so uniform or striking
as mine.

and of unequal sizes. I observed, under the
circumstances immediately to be stated, the number of seeds produced by
six plants (Exp. I to VI.) in the first lot of eight plants,
and by three plants in each of the other two lots belonging to the
present class.

Experiment I. This long-styled plant was
allowed during 1863 to be freely and legitimately fertilized by an
adjoining illegitimate mid-styled plant, but it did not yield a single
seed-capsule. It was then removed and planted in a remote place close
to a brother long-styled plant No. II., so that it must have been
freely though illegitimately fertilized; under these circumstances it
did not yield during 1864 and 1865 a single capsule. I should here
state that a legitimate or ordinary long-styled plant, when
growing isolated and freely, though illegitimately fertilized by
insects with its own pollen, yielded an immense number of capsules,
which contained on an average 21.5 seeds.

Exp. II. This long-styled plant, after
flowering during 1863 close to an illegitimate mid-styled plant,
produced less than twenty capsules, which contained on an average
between four and five seeds. When subsequently growing in company with
No. I., by which it will have been illegitimately fertilized,
it
yielded in 1866 not a single capsule, but in 1865 it yielded twenty-two
capsules: the best of these, fifteen in number, were examined; eight
contained no seed, and the remaining seven contained on an average only
three seeds, and these seeds were so small and shrivelled that I doubt
whether they would have germinated.

Exp. III. & IV. These two
long-styled plants, after being freely and legitimately fertilized by
the same illegitimate mid-styled plant during 1863 were as miserably
sterile as No. II.

Exp. V. This long-styled plant, after
flowering in 1863 close to the illegitimate mid-styled plant, yielded
only four capsules, which altogether included only five seeds. During
1864, 1865, and 1866, it was surrounded either by illegitimate or
legitimate plants of the other two forms; but it did not yield a single
capsule. It was a superfluous experiment, but I likewise artificially
fertilized in a legitimate manner twelve flowers; but not one produced
a capsule; so that this plant is almost absolutely barren.

Exp. VI. This long-styled plant, after
flowering during the favourable year of 1866, surrounded by
illegitimate plants of the other two forms, did not produce a single
capsule.

Exp. VII. This long-styled plant was the most
fertile of the eight plants of the first lot. During 1865 it was
surrounded by illegitimate plants of various parentage, many of which
were highly fertile,

and must thus have been legitimately fertilized. It
produced a good many capsules, ten of which yielded an average of 36.1
seeds, with a maximum of 47 and a minimum of 22; so that this plant
produced 39 per cent. of the full number of seeds. During 1864 it was
surrounded by legitimate and illegitimate plants of the other two
forms; and nine capsules (one poor one being rejected) yielded an
average of 41.9 seeds, with a maximum of 56, and a minimum of 28; so
that, under these favourable circumstances, this plant, the most
fertile of the first lot, did not yield, when legitimately fertilized,
quite 45 per cent. of the full complement of seeds.

In the second lot of plants in the present class,
descended from the long-styled form fertilized by its own pollen, and
almost certainly from the longer stamens, the plants, as already
stated, were not nearly so dwarfed or so sterile as in the first lot.
All produced plenty of capsules. I counted the number of seeds in only
three plants, viz. Nos. VIII., IX., & X.

Exp. VIII. This plant was allowed to be
freely fertilized in 1864 by legitimate and illegitimate plants of the
other two forms, and yielded from ten capsules an average of 41.1
seeds, with a maximum of 73 and a minimum of 11. Hence this
plant produced only 44 per cent. of the full complement of seeds.

Exp. IX. This long-styled plant was allowed
in 1865 to be freely fertilized by illegitimate plants of the other two
forms, most of which were moderately fertile. Fifteen capsules yielded
an average of 57.1 seeds, with a maximum of 86 and a minimum of 23.
Hence the plant yielded 61 per cent. of the full complement of seeds.

Exp. X. This long-styled plant was freely
fertilized at the same time and in the same manner as the last. Ten
capsules yielded an average of 44.2 seeds, with a maximum of 69 and a
minimum of 25; hence this plant yielded 47 per cent. of the full
complement of seeds.

The nineteen long-styled plants of the third lot, of
the same parentage as the last lot, were treated differently; for they
flowered during 1867 by themselves, so that they must have been
illegitimately fertilized by each other. It has already been stated
that a legitimate long-styled plant, growing by itself and visited by
insects, yielded an average of 21.5 seeds per capsule, with a maximum
of 35; but, to judge fairly of its fertility, this plant, as well as
others, ought to have been observed during successive seasons. We may
infer from analogy that, if several legitimate long-styled plants were
to fertilize each other, the average number

of seeds would be increased; but how much increased I
do not know; hence I have no perfectly fair standard of comparison by
which to judge of the fertility of the three following plants of the
present lot, the seeds of which I counted.

Exp. XI. This long-styled plant produced a
large crop of capsules, and seemed to be one of the most fertile of the
whole lot of nineteen plants. The average from ten capsules was 35.9
seeds, with a maximum of 60 and a minimum of 8.

Exp. XII. This and the following long-styled
plant produced very few capsules; ten yielded an average of only 15.4
seeds, with a maximum of 30 and a minimum of 4.

Exp. XIII. This plant offers an anomalous
case; for it flowered profusely, but produced very few capsules; yet
these capsules contained numerous seeds. Ten capsules yielded an
average of 71.9 seeds, with a maximum of 95 and a minimum of 29.
Considering that this plant was illegitimate, and illegitimately
fertilized by its brother long-styled seedlings, the average and the
maximum are so remarkably high that I cannot at all understand the case.

CLASS II. Illegitimate plants from the
short-styled form, fertilized by pollen from the shorter stamens of the
same form.

I raised from this union nine plants, of which eight
were short-styled and one long-styled; so that there seems to be a
strong tendency with this form to reproduce, when self-fertilized, the
parent form; but the tendency is not so strong as with the long-styled.
These nine plants never attained the full height of legitimate plants
growing close to them. The anthers in many of the flowers on several
plants were contabescent.

Exp. XIV. This short-styled plant was allowed
during 1865 to be freely and legitimately fertilized by illegitimate
plants descended from self-fertilized mid-, long- and short-styled
plants. Fifteen capsules yielded an average of 28.3 seeds, with a
maximum of 51 and a minimum of 11. The seeds themselves were small and
irregular in shape; hence this plant produced only 33 per cent. of the
proper number of seeds. Although so sterile on the female side, none of
its anthers were contabescent.

Exp. XV. This short-styled plant, treated
like the last during the same year, yielded an average, from fifteen
capsules, of 27 seeds with a maximum of 49 and a minimum of 7. But two
poor capsules may be rejected, and then the average rises to 32.6, with
the same maximum of 49 and a minimum of 20; so that this plant attained
38 per cent. of the normal standard of fertility

and was rather more fertile than the last, yet many of
the anthers were contabescent.

Exp. XVI. This short-styled plant, treated
like the two last, yielded from ten capsules an average of 77.8 seeds,
with a maximum of 97 and a minimum of 60; so that this plant produced
94 per cent. of the full number of seeds.

Exp. XVII. This, the one long-styled plant of
the same parentage as the last three plants, when freely and
legitimately fertilized in the same manner as the last, yielded an
average from ten capsules of 76.3 rather poor seeds, with a maximum of
88 and a minimum of 57. Hence this plant produced 82 per cent. of the
proper number of seeds. Twelve flowers under a net were artificially
and legitimately fertilized by pollen from a legitimate short-styled
plant; and nine capsules yielded an average of 82.5 seeds, with a
maximum of 98 seeds and a minimum of 51; so that its fertility was
increased by the action of pollen from a legitimate plant, but still
did not reach the normal standard.

CLASS III. Illegitimate plants from the mid-styled
form fertilized by pollen from the longer stamens of the same form.

After two trials, I succeeded in raising only four
plants from this illegitimate union. These proved to be three
mid-styled and one long-styled; but from so small a number we can
hardly judge of the tendency in mid-styled plants when self-fertilized
to reproduce the same form. These four plants never attained their full
and normal height; the long-styled plant had several of its anthers
contabescent.

Exp. XVIII. This mid-styled plant, when
freely and legitimately fertilized during 1865 by illegitimate plants
descended from self-fertilized long-, short-, and mid-styled plants,
yielded an average from ten capsules of 102.6 seeds, with a maximum of
131 and a minimum of 63: hence this plant did not produce quite 80 per
cent. of the normal number of seeds. Twelve flowers were artificially
and legitimately fertilized by pollen from a legitimate long-styled
plant, and yielded from nine capsules an average of 116.1 seeds, which
were finer than in the previous case, with a maximum of 135 and a
minimum of 75; so that, as in Exp. XVII., pollen from a
legitimate plant increased the fertility, but did not bring it up to
the full standard.

Exp. XIX. This mid-styled plant, fertilized
in the same manner and at the same period with the last, yielded an
average from ten capsules of 73.4 seeds, with a maximum of 87 and a
minimum of 64; hence this plant produced only 56 per cent. of the full
number

of seeds. Thirteen flowers were artificially and
legitimately fertilized by pollen from a legitimate long-styled plant,
and yielded ten capsules with an average of 95.6 seeds; so that the
application of pollen from a legitimate plant added, as in the two
previous cases, to the fertility, but did not bring it up to the proper
standard.

Exp. XX. This long-styled plant, of the same
parentage with the last two mid-styled plants, and freely fertilized in
the same manner, yielded an average from ten capsules of 69.6 seeds,
with a maximum of 83 and a minimum of 52; hence the plant produced 75
per cent. of the full number of seeds.

CLASS IV. Illegitimate plants from the
short-styled form fertilized by pollen from the longer stamens of the
long-styled form.

In the three previous classes, plants raised from the
three forms fertilized by pollen from either the longer or shorter
stamens of the same form, but not of the same individual plant, have
been described. Six other illegitimate unions are possible, namely
between the three forms and the stamens in the other two forms which do
not correspond in height with the pistil. But I succeeded in raising
plants from only three of these six unions. From one of them, forming
the present Class, twelve plants were raised; these consisted of eight
short-styled, and four long-styled plants, with not one mid-styled.
These twelve plants never attained quite their full and proper height,
but by no means deserved to be called dwarfs. The anthers in some of
the flowers were contabescent. One plant was remarkable from all the
longer stamens in every flower and from many of the shorter stamens
having their anthers in this condition. The pollen of four other
plants, in which none of the anthers were contabescent. was examined;
in one a moderate number of grains were minute and shrivelled, but in
the other three they appeared perfectly sound. With respect to the
power of producing seed, five plants (Exps. XXI. to XXV.)
were observed: one yielded scarcely more than half the normal number; a
second was slightly infertile; but the three others actually produced a
larger average number, with a higher maximum, than the standard. In my
concluding remarks on Lythrum I shall recur to this fact,
which at first appears inexplicable.

Exp. XXI. This short-styled plant, freely and
legitimately fertilized during 1865 by illegitimate plants, descended
from self-fertilized long-, mid- and short-styled parents, yielded an
average from ten capsules of 43 seeds, with a maximum of 63 and a
minimum of 26; hence this plant, which was the one with all its

longer and many of its shorter stamens contabescent,
produced only 52 per cent. of the proper number of seeds.

Exp. XXII.—This short-styled plant produced
perfectly sound pollen, as viewed under the microscope. During 1866 it
was freely and legitimately fertilized by other illegitimate plants
belonging to the present and the following class, both of which include
many highly fertile plants. Under these circumstances it yielded from
eight capsules an average of 100.5 seeds, with a maximum of 123 and a
minimum of 86; so that it produced 121 per cent. of seeds in comparison
with the normal standard. During 1864 it was allowed to be freely and
legitimately fertilized by legitimate and illegitimate
plants, and yielded an average, from eight capsules, of 104.2 seeds,
with a maximum of 125 and a minimum of 90; consequently it produced 125
per cent. of the normal standard. In this case, as in some previous
cases, pollen from legitimate plants added in a small degree to the
fertility of the plant; and the fertility would, perhaps, have been
still greater had not the summer of 1864 been very hot, and certainly
unfavourable to some of the plants of Lythrum.

Exp. XXIII.—This short-styled plant
produced perfectly sound pollen. During 1866 it was freely and
legitimately fertilized by the other illegitimate plants specified
under the last experiment, and yielded an average, from eight capsules,
of 113.5 seeds, with a maximum of 123 and a minimum of 93. Hence this
plant produced no less than 136 per cent. of the normal standard.

Exp. XXIV.—This long-styled plant produced
pollen which seemed under the microscope sound; but some of the grains
did not swell when placed in water. During 1864 it was legitimately
fertilized by legitimate and illegitimate plants in the
manner described under Exp. XXII., but yielded an average, from ten
capsules, of only 55 seeds, with a maximum of 88 and a minimum of 24,
thus attainining 59 per cent. of the normal fertility. This
low degree of fertility, I presume, was owing to the unfavourable
season; for during 1866, when legitimately fertilized by illegitimate
plants in the manner described under Exp. XXII., it yielded an
average, from eight capsules, of 82 seeds, with a maximum of 120 and a
minimum of 67, thus producing 88 per cent. of the normal number of
seeds.

Exp. XXV.—The pollen of this long-styled
plant contained a moderate number of poor and shrivelled grains; and
this is a surprising circumstance, as it yielded an extraordinary
number of seeds. During 1866 it was freely and legitimately fertilized
by

illegitimate plants, as described under Exp. XXII., and
yielded an average, from eight capsules, of 122.5 seeds, with a maximum
of 149 and a minimum of 84. Hence this plant produced no less than 131
per cent. of the normal standard.

CLASS V.—Illegitimate plants from the mid-styled
form, fertilized by pollen from the shorter stamens of the
long-styled
form.

I raised from this union twenty-five plants, which
proved to be seventeen long-styled and eight mid-styled, but not one
short-styled. None of these plants were in the least dwarfed. I
examined, during the highly favourable season of 1866, the pollen of
four plants: in one mid-styled plant, some of the anthers of the longer
stamens were contabescent, but in the other anthers the pollen-grains
were mostly sound, as they were in all the anthers of the shorter
stamens; in two other mid-styled and in one long-styled plant many of
the pollen grains were small and shrivelled; and in the latter plant as
many as a fifth or sixth appeared to be in this state. I counted the
seeds in five plants (Exp. XXVI. to XXX.), of which two were moderately
sterile and three fully fertile.

Exp. XXVI.—This mid-styled plant was freely
and legitimately fertilized, during the rather unfavourable year 1864,
by numerous surrounding legitimate and illegitimate plants. It yielded
an average, from ten capsules, of 83.5 seeds, with a maximum of 110 and
a minimum of 64, thus attaining 64 per cent. of the normal fertility.
During the highly favourable year 1866, it was freely and
legitimately fertilized by illegitimate plants belonging to the present
Class and to Class IV., and yielded an average, from eight capsules, of
86 seeds, with a maximum of 109 and a minimum of 61, and thus attained
66 per cent. of the normal fertility. This was the plant with
some of the anthers of the longer stamens contabescent as above
mentioned.

Exp. XXVII.—This mid-styled plant, fertilized
during 1864 in the same manner as the last, yielded an average, from
ten capsules, of 99.4 seeds, with a maximum of 122 and a minimum of 53,
thus attaining to 76 per cent. of the normal fertility. If
the season had been more favourable, its fertility would probably have
been somewhat greater, but, judging from the last experiment, only in a
slight degree.

Exp. XXVIII.—This mid-styled plant, when
legitimately fertilized during the favourable season of 1866, in the
manner described under Exp. XXVI., yielded an average, from eight
capsules, of 89 seeds, with a maximum of 119 and a minimum of 69, thus

producing 68 per cent. of the full number of seeds. In
the pollen of both sets of anthers, nearly as many grains were small
and shrivelled as sound.

Exp. XXIX.—This long-styled plant was
legitimately fertilized during the unfavourable season of 1864, in the
manner described under Exp. XXVI., and yielded an average, from ten
capsules, of 84.6 seeds, with a maximum of 132 and a minimum of 47,
thus attaining to 91 per cent. of the normal fertility. During
the highly favourable season of 1866, when fertilized in the manner
likewise described under Exp. XXVI., it yielded an average, from nine
capsules (one poor capsule having been excluded), of 100 seeds, with a
maximum of 121 and a minimum of 77. This plant thus exceeded the normal
standard, and produced 107 per cent. of seeds. In both sets of anthers
there were a good many bad and shrivelled pollen-grains, but not so
many as in the last-described plant.

Exp. XXX.—This long-styled plant was
legitimately fertilized during 1866 in the manner described under Exp.
XXVI., and yielded an average, from eight capsules, of 94 seeds, with a
maximum of 106 and a minimum of 66; so that it attained 101 per cent.
of the normal fertility.

Exp. XXXI.—Some flowers on this long-styled
plant were artificially and legitimately fertilized by one of its
brother mid-styled plants; and five capsules yielded an average of 90.6
seeds, with a maximum of 97 and a minimum of 79. Hence, as far as can
be judged from so few capsules, this plant attained, under these
favourable circumstances, 98 per cent. of the normal standard.

CLASS VI.—Illegitimate plants from the mid-styled
form fertilized by pollen from the longer stamens of the short-styled
form.

I have shown, in my former paper on Lythrum
Salicaria, that the union from which these illegitimate plants
were derived is far more fertile than any other illegitimate union; for
the mid-styled parent, when thus fertilized, yielded an average (all
very poor capsules being excluded) of 102.8 seeds, with a maximum of
130; and the plants in the present class accord in character with the
but slightly lessened fertility of the parent-union. I raised forty
plants; and these attained their full height and were covered with
seed-capsules. Nor did I observe any contabescent anthers. It deserves,
also, particular notice that these plants, differently from what occurs
in any previous class, consisted of all three forms, namely eighteen
short-styled, fourteen long-styled, and eight mid-styled plants. From
these circumstances, I counted the seed in

Exp. XXXII.—This mid-styled plant was
freely and legitimately fertilized, during the rather unfavourable year
of 1864, by numerous surrounding legitimate and illegitimate plants.
Eight capsules yielded an average of 127.2 seeds, with a maximum of 144
and a minimum of 96; so that this plant attained 98 per cent. of the
normal standard.

Exp. XXXIII.—This short-styled plant was
fertilized in the same manner and at the same time with the last; and
ten capsules yielded an average of 113.9, with a maximum of 137, and a
minimum of 90. Hence this plant produced no less than 137 per cent. of
seeds in comparison with the standard.

Concluding remarks on the illegitimate offspring
of the three forms of Lythrum salicaria.

From the three forms occurring in approximately equal
numbers in a state of nature, and from the results of sowing seed
naturally produced, there is reason to believe that each form when
legitimately fertilized, reproduces all three forms in about equal
numbers. Now we have seen (and the fact is a very singular one) that
the fifty-six plants produced from the long-styled form, when
illegitimately fertilized by pollen from the same form (Class I.), were
all long-styled. The short-styled form, when self-fertilized (Class
II.), produced eight short-styled and one long-styled plant; and the
mid-styled form, similarly treated (Class III.), produced three
mid-styled and one long-styled offspring; so that these two forms, when
illegitimately fertilized by pollen from the same form, evince a
strong, but not exclusive, tendency to reproduce the parent-form. When
the short-styled form was illegitimately fertilized by the long-styled
form (Class IV.), and again when the mid-styled was illegitimately
fertilized by the long-styled (Class V.), in each case the two
parent-forms alone were reproduced. As thirty-seven plants were raised
from these two unions, we may, with much confidence, believe that it is
the rule that plants thus produced yield both parent-forms but not the
third form. When, however, the mid-styled form was illegitimately
fertilized by the short-styled (Class VI.), the same rule did not hold
good; for the seedlings consisted of all three forms, but in unequal
numbers. Nor is this exception surprising; for the illegitimate union
from which these seedlings were derived is, as previously stated,

singularly fertile, and the seedlings themselves
exhibit no signs of sterility, and grow to their full height.

Tabulated results of the fertility of the foregoing
illegitimate plants, when legitimately fertilized, generally by
illegitimate plants, as described under each experiment. Experiments
XI., XII., & XIII. are excluded; for these plants were
illegitimately fertilized.

Number
of
Experiment and
Standard.

Form.

Average
number of
seeds produced.

Maximum
number in
any one
capsule.

Minimum
number in
any one
capsule.

Calculated
average
of seeds
relatively to the normal standard, this being taken in each case as 100.

Standard ……..

Long-styled

93

159

No
record
was kept; but
all excessively poor capsules were rejected.

Do ……

Mid-styled…

130

151

Do ……

Short-styled

83.5

112

CLASS I.—Illegitimate plants from the long-styled
form, fertilized by pollen from the longer or shorter stamens of the
same form.

Experiment
I.

Long-styled

0

0

0

0

II.

Do.

4.5

…

…

5

III.

Do.

4.5

…

…

5

IV.

Do.

4.5

…

…

5

V.

Do.

0 or 1

…

…

0 or 1

VI.

Do.

0

…

…

0

VII.

Do.

36.1

47

22

39

VIII.

Do.

41.1

73

11

44

IX.

Do.

57.1

86

23

61

X.

Do.

44.2

69

25

47

CLASS II.—Illegitimate plants from the
short-styled form, fertilized by pollen from the shorter stamens of the
same form.

Exp.
XIV.

Short-styled

28.3

51

11

33

XV.

Do.

32.6

49

20

38

XVI.

Do.

77.8

97

60

94

XVII.

Long-styled

76.3

88

57

82

CLASS III.—Illegitimate plants from the
mid-styled form, fertilized by pollen from the longer stamens of the
same form.

CLASS IV.—Illegitimate plants from the
short-styled form, fertilized by pollen from the longer stamens of the
long-styled form.

Number
of
Experiment.

Form.

Average
number of
seeds produced.

Maximum
number in
any one
capsule.

Minimum
number in
any one
capsule.

Calculated
average
of seeds
relatively to the normal standard, this being taken in each case as 100.

Exp. XXI.

Short-styled

43.0

63

26

52

XXII.

Do.

100.5

123

86

121

XXIII.

Do.

113.5

123

93

136

XXIV.

Long-styled

82.0

120

67

88

XXV.

Do.

122.5

149

84

131

CLASS V.—Illegitimate plants from the mid-styled
form, fertilized by pollen from the shorter stamens of the long-styled
form.

Exp.
XXVI.

Mid-styled

86.0

109

61

66

XXVII.

Do.

99.4

122

53

76

XXVIII.

Do.

89.0

119

69

68

XXIX.

Long-styled

100.0

121

77

107

XXX.

Do.

94.0

106

66

101

XXXI.

Do.

90.6

97

79

98

CLASS VI.—Illegitimate plants from the mid-styled
form, fertilized by pollen from the longer stamens of the short-styled
form.

Exp.
XXXII.

Mid-styled

127.2

144

96

98

XXXIII.

Short-styled

113.9

137

90

137

The lessened fertility of most of these illegitimate
plants is in many respects a highly remarkable phenomenon. Thirty-three
plants in the six classes were subjected to various trials, and the
seeds carefully counted. Some were artificially fertilized, but the far
greater number were freely fertilized (and this is the better and
natural plan) through the agency of insects, by other illegitimate
plants. In the right-hand or percentage column in the accompanying
Table, a wide difference in fertility between the plants in the first
three and the last three classes may be perceived. In the first three
classes the plants are descended from the three forms illegitimately
fertilized by pollen taken from the same form, but not from the same
individual plant. It is necessary to observe this latter circumstance;
for, as I shall at some future time show*, most plants, independently
of dimor-

* I have given a brief abstract of some
of these observations in my work on 'The Variation of Animals and
Plants under Domestication,' 1867, vol. ii. p. 128.

phism or trimorphism, when fertilized with their own
pollen, are in some degree dwarfed, and sometimes rendered sterile.
None of the nineteen plants in the first three classes attained
complete fertility; one, however, made a near approach, yielding 96 per
cent. of the proper number of seeds. From this high degree of fertility
we have many descending gradations, till we reach an absolute zero,
when the plants, though bearing many flowers, did not produce, during
successive years, a single seed or even seed-capsule. Some of the most
sterile plants did not yield a single seed, even when legitimately
fertilized by pollen from legitimate plants. The first seven plants in
Class I., which are by far the most sterile, probably ought to form a
distinct class from the three following plants; for there is reason to
suspect that the former are the product of the shorter stamens of the
long-styled form, whilst it is almost certain that the latter are
descended from the longer stamens of the same form; but, owing to this
doubt, they are all arranged under the same class. The several classes
differ in their average degree of fertility; and in the same class
there is a wide difference in the fertility of the several plants,
though descended from the same parents, sown at the same time, and
grown in the same soil. None of the plants in the first three classes
attained their full and proper stature; the first seven plants, which,
as already stated, probably ought to form a distinct class, are by far
the most dwarfed, several of them never reaching to half their proper
height. These same plants did not flower at so early an age, or so
early in the season, as they ought to have done. The anthers in many of
their flowers, and in the flowers of some other plants in the first
five classes, were either contabescent or included numerous small and
shrivelled pollen-grains. As the suspicion at one time occurred to me
that the lessened fertility of all the illegitimate plants might be due
to the pollen alone being affected, I may remark that this is certainly
not the case; for several of them, when fertilised by sound pollen from
legitimate plants, did not yield the full complement of seeds; hence it
is certain that both the female and male reproductive organs are
affected.

Turning now to the fourth, fifth, and sixth classes,
and looking to the right-hand column of the Table, we find nearly as
many plants with a percentage of seeds above the standard as beneath
it. Hence, at first sight, it appears probable that the number of seeds
ordinarily produced is much more variable than I have supposed, and,
consequently, that the plants in these three classes do not really
differ

in their power of yielding seed, but have merely varied
temporarily in fertility. Nevertheless we may reject this conclusion as
far as the less fertile plants are concerned,—first, because none of
the plants in Class IV. attained their proper height, which shows that
they were in some manner affected; and, secondly, because many of the
plants in Classes IV. & V. produced anthers which were either
contabescent or included small and shrivelled pollen-grains. And as in
these cases the male organs were manifestly deteriorated, it is by far
the most probable conclusion that the female organs were likewise
affected, and that this was the cause of the reduced number of seeds.

With respect to the three short-styled and three
long-styled plants in the three latter classes, which yield too high a
percentage of seeds, the explanation is much more doubtful. The normal
standard for the long-styled form was deduced by counting the seeds in
twenty-three capsules, and for the short-styled form from twenty-five
capsules. I do not pretend that this is a sufficient number of capsules
for absolute accuracy; but my experience leads me to believe that a
very fair result would thus be gained. As, however, the maximum number
observed in the twenty-five capsules of the short-styled form is low,
the standard in this case may possibly be not quite high enough. In the
case of the illegitimate plants, in order to avoid overestimating their
infertility, ten very fine capsules were always selected; and the years
1865 and 1866, during which the plants in the three latter classes were
observed, were highly favourable for seed production. Now, if this plan
of selecting very fine capsules during favourable seasons had been
followed for obtaining the normal standards, instead of taking, during
various seasons, the first capsules which came to hand, the standards
would undoubtedly have been considerably higher; and thus the fact of
the six foregoing plants appearing to yield an unnaturally high
percentage of seeds may, perhaps, be accounted for. On this view, these
plants are, in fact, merely fully fertile, and not fertile to an
abnormal degree. Nevertheless, as characters of all kinds are liable to
variation, especially with organisms unnaturally treated, and as in the
three first and more sterile classes, the plants derived from the same
parents, and treated in the same manner, certainly did vary much in
sterility, it is possible that certain plants, in the latter and more
fertile classes, may have varied so as to have acquired an abnormal
degree of fertility. But it should be especially observed
that, if my standards err in being too low, the sterility of all the
many sterile

plants in the several classes, will have to be
estimated higher in the same proportion. Finally, we see that the
illegitimate plants in the three first classes are all more or less
sterile, some being absolutely barren, with one alone almost completely
fertile; in the three latter classes, some of the plants are moderately
sterile, whilst others are fully fertile or possibly fertile in excess.

The last point which need here be noticed is that, as
far as my means of comparison serve, a certain degree of relation
exists between the infertility of the illegitimate first unions between
the several forms and that of their illegitimate offspring. Thus the
two illegitimate unions, from which the seedlings in Classes V. &
VI. were derived, yielded a fair amount of seed, and only a few of
these plants are in any degree sterile. On the other hand, the
illegitimate unions between plants of the same form always yield very
few seeds, and their seedlings are the most sterile. But the relation
is not strict; for the first six or seven plants in the Table were
extremely sterile, out of all proportion to the union from which they
were derived. There is also a tolerably close parallelism in each class
between the degree of sterility and the dwarfed stature of the plants.
As previously stated, an illegitimate plant fertilized by pollen from a
legitimate plant has its fertility slightly increased. The importance
of the several foregoing conclusions will be apparent at the close of
this paper, when the illegitimate unions between the forms of the same
species, and their illegitimate offspring, are compared in functional
power with the hybrid unions and the hybrid offspring of distinct
species.

Genus OXALIS.

Dr. Hildebrand* has proved that Oxalis rosea is
a trimorphic species, like Lythrum Salicaria. He possessed
in the living state the long-styled form alone, and from its seeds,
necessarily self-fertilized, he raised seedlings which proved all
long-styled; but, unfortunately, he does not state how many plants were
raised.

illegitimately fertilized by pollen from the same form,
twenty-seven seedlings. These were all long-styled. They proved fully
fertile or even fertile in excess; for ten flowers, fertilized by
pollen from other plants of the same lot, yielded nine capsules,
containing on an average 39.75 seeds, with a maximum number in one
capsule of sixty-six seeds. Again four of these flowers legitimately
crossed by pollen from a legitimate plant, and four flowers on the
latter crossed by pollen from the illegitimate seedlings, yielded seven
capsules with an average of fifty-three seeds, with a maximum of
seventy-two. I must here state that I have found some difficulty in
estimating the standard of fertility for the several unions of this
species, as the results differed much during successive years*, and the
seeds vary so greatly in size that it is hard to decide which ought to
be considered good. In order to avoid overestimating the infertility of
the several illegitimate unions, I have taken as low standards as
possible.

From the foregoing twenty-seven plants, fertilized by
their own-form pollen, I raised twenty-five seedling grandchildren; and
these were all long-styled; so that from the two illegitimate
generations fifty-two plants were raised, and all without exception
proved long-styled. These grandchildren grew vigorously and soon
exceeded in height two other lots of illegitimate seedlings of
different parentage and one lot of equal-styled seedlings presently to
be described. Hence I expected that they would turn out highly
ornamental plants; but when they flowered, they seemed, as my gardener
remarked, to have gone back to the wild state; for the petals were
pale-coloured, narrow, sometimes not touching each other, flat,
generally deeply notched in the middle, but not flexuous on the margin,
and with the yellow eye

* Dr. Hildebrand was much more
successful than I was in fertilizing the flowers of P. sinensis;
yet the number of seeds obtained by him is certainly much too low. Thus
he gives (Bot. Zeitung, 1864, p. 3) eighteen seeds as the average
number produced by the long-styled form, when illegitimately fertilized
by the same-form pollen, and forty-one as the number when legitimately
fertilized. For the short-styled form, the corresponding numbers are
twenty and forty-four. The lowest standards which I can give for the
illegitimate and legitimate unions of the long-styled form are
thirty-five and at least fifty, and for the short-styled at least
twenty-five and sixty-four. It is possible that Dr. Hildebrand's plants
were grown in too small pots, or, whilst maturing their seeds, were
otherwise treated in an unfavourable manner. This would account for the
greater inequality observed by him than that by me between the product
of seeds from the legitimate and illegitimate unions, as the latter
always suffer most from unfavourable conditions.

or centre conspicuous. Altogether these flowers, in
comparison with those of their progenitors, presented a striking
difference, which can, I think, be accounted for only on the principle
of reversion. One of these grandchildren had most of its anthers
contabescent. Seventeen of the flowers were illegitimately fertilized
by pollen taken from seedlings of the same lot, and produced fourteen
capsules, containing on an average 29.2 seeds; they ought to have
contained about thirty-five seeds. Fifteen flowers legitimately
fertilized by pollen from an illegitimate short-styled plant (belonging
to the lot next to be described) produced fourteen capsules, containing
an average of forty-six seeds; they ought to have contained at least
fifty seeds. Hence these grandchildren of illegitimate descent appear
to have lost, though only in a very slight degree, their full fertility.

From a short-styled form of P. sinensis,
fertilized by its own-form pollen, I raised, during February 1862,
eight seedlings, seven of which were short-styled and one long-styled.
These plants grew slowly, and never attained to the full stature of
ordinary plants; some of them flowered precociously, and others late in
the season. Four flowers on the short-styled plants and four on the
long-styled plant were illegitimately fertilized with their own-form
pollen and produced only three capsules, containing on an average 23.6
seeds, with a maximum of twenty-nine; but we cannot judge of their
fertility from so few capsules; and I have greater doubts about the
normal standard for this union than about the standard for the three
other unions; but I believe that rather above twenty-five seeds would
be a fair estimate. Eight flowers on the short-styled and long-styled
illegitimate plants were reciprocally and legitimately crossed; they
produced five capsules which contained an average of 28.6 seeds, with a
maximum of thirty-six. A reciprocal cross between legitimate plants of
the two forms would have yielded an average of at least fifty-seven
seeds, with a possible maximum of seventy-four seeds; so that these
illegitimate plants are sterile when legitimately crossed.

I succeeded in raising from the seven short-styled
illegitimate plants, fertilized by their own-form pollen, only six
plants—grandchildren of the first union. These, like their parents,
were of low stature, and had so poor a constitution that four died
before flowering. With ordinary plants it has been a rare event with me
to have more than a single plant die out of a large lot. The two
grandchildren which lived and flowered were short-styled; and twelve of
their flowers were fertilized with their own-form pollen

and produced twelve capsules containing an average of
28.2 seeds; so that these two plants, though belonging to so weakly a
set, were rather more fertile than their parents, and perhaps not at
all sterile. Four flowers on the same two grandchildren were
legitimately fertilized by a long-styled illegitimate plant, and
produced four capsules, containing only 32.2 seeds instead of about
sixty-four seeds, which is the normal average I have obtained from
legitimate short-styled plants legitimately crossed.

By looking back, it will be seen that at first I raised
from a short-styled plant fertilized by its own-form pollen seven
short-styled plants and one-long styled. These illegitimate plants of
the two forms were legitimately crossed, and from their seed fifteen
plants were raised, grandchildren of the first illegitimate union.
According to analogy half of them ought to have been long-styled and
half short-styled; but all were short-styled. Altogether, of the
twenty-five plants illegitimately descended from the short-styled
grandparent, twenty-four proved to be short-styled and one alone
long-styled. Twelve short-styled flowers borne by the fifteen
grandchildren were fertilized by pollen taken from plants of the same
form belonging to the same lot, and produced eight capsules which
contained an average of 21.8 seeds, with a maximum of thirty-five.
These figures are rather below the normal standard for such a union.
Six flowers were also legitimately fertilized by an illegitimate
long-styled plant and produced only three capsules, containing on an
average 23.6 seeds with a maximum of thirty-five. Such a union in the
case of a legitimate plant ought to have yielded an average of
sixty-four seeds, with a possible maximum of seventy-three seeds.

Summary on the transmission of form, constitution,
and fertility of the illegitimate offspring of Primula
sinensis.—In regard to the long-styled form, the illegitimate
offspring, as far as my experience during two generations of fifty-two
plants serves*, appear invariably to be long-styled. These plants grew
vigorously; but the flowers in one instance were small, appearing as if
they had reverted to the wild state. In the first illegitimate
generation they were perfectly fertile, and in the second their
fertility was only very slightly impaired. With respect to the
short-styled

* Dr. Hildebrand (Bot. Zeitung, 1864, p.
5) raised from a similar illegitimate union seventeen plants, of which
fourteen were long-styled and three short-styled. From a short-styled
plant illegitimately fertilized by its own pollen he raised fourteen
plants, of which eleven were short-styled and three long-styled.

form, twenty-four out of twenty-five of their
illegitimate offspring were short-styled. They were dwarfed in stature,
and one lot of grandchildren had so poor a constitution that four out
of six plants perished before flowering. The two survivors, when
illegitimately fertilized by their own-form pollen, were rather less
fertile than they ought to have been; but their loss of fertility was
clearly shown in a special and unexpected manner, namely when
legitimately fertilized by other illegitimate plants: thus altogether
eighteen flowers fertilized in this manner yielded twelve capsules,
which included on an average only 28.5 seeds, with a maximum of
forty-five. Now a legitimate short-styled plant would have yielded,
when legitimately fertilized, an average of sixty-four seeds, with a
possible maximum of seventy-four. This particular kind of infertility
will perhaps be best appreciated by a simile: we may assume that six
children would on an average be born from each ordinary marriage; but
that only three would be born from an incestuous marriage. Now,
according to the analogy of Primula sinensis, the children of
such incestuous marriages, if they continued to marry incestuously,
would have their sterility only slightly increased; but their fertility
would not be restored by a proper marriage; for if two children, both
of incestuous origin, but in no degree related to each other, were to
marry, the marriage would of course be strictly legitimate,
nevertheless they would not give birth to more than half the full and
proper number of children.

Equal-styled variety of Primula sinensis.—As
any variation in the structure of the reproductive organs, combined
with changed function, is a rare event, the following cases are worth
giving in detail. Mr. Scott, in his excellent paper on the reproductive
functions in the Primulaceæ*, has recorded some analogous facts. My
attention was first called to the subject by observing, in 1862, a
long-styled plant, descended from a self-fertilized long-styled parent,
with some of its flowers in an anomalous state, namely, with the
stamens placed low down in the corolla as in the ordinary long-styled
form, but with the pistils so short that the stigmas stood on a level
with the anthers. These stigmas were nearly as globular and as smooth
as in the short-styled form, instead of being elongated and rough as in
the long-styled form. Here, then, we have stamens of the long-styled
form and a pistil closely resembling that of the short-styled form
combined in the same flower. But

the structure varied much on the same umbel: for in two
flowers the pistil was intermediate in length between that of the
long- and that of the short-styled form, with the stigma elongated as
in
the former, and smooth as in the latter; and in three other flowers the
structure was in all respects like that of the long-styled form. These
modifications appeared to me so remarkable that I fertilized eight of
the flowers with their own pollen, and obtained five capsules, which
contained on an average forty-three seeds; and this number shows that
the flowers had become abnormally fertile in comparison with those of
ordinary long-styled plants when self-fertilized. These facts led me to
examine the plants in several small collections, with the following
result, showing that the equal-styled variety is not rare.

Name of
Owner or Place.

Long-styled
Form.

Short-styled
Form.

Equal-styled
Variety.

Mr. Horwood ……

0

0

17

Mr Duck ……..

20

0

9

Baston …

30

18

15

Chichester…….

12

9

2

Holwood……..

42

12

0

High Elms………

16

0

0

Westerham……

1

5

0

My own plants from purchased
seeds…

13

7

0

Total …………

134

51

43

In a state of nature the long- and short-styled forms
would no doubt occur in equal numbers, as I infer from the analogy of
other dimorphic species of Primula, and from having raised
the two forms of the present species in exactly the same number from
flowers which had been legitimately crossed. The
preponderance in the above Table of the long-styled form over the
short-styled (in the proportion of 134 to 51) results from gardeners
generally collecting seed from self-fertilized flowers; and I have
shown in my previous paper that the long-styled form spontaneously
produces much more seed than the short-styled, owing to the anthers in
the long-styled form being placed low down in the corolla, so that,
when the flowers fall off, the anthers are dragged over the stigma; and
we now also know that long-styled plants, when self-fertilized, almost
invariably reproduce long-styled offspring.

To return to the equal-styled variety. Mr.
Horwood raised from purchased seed four plants, which certainly were
not long-

styled, but were either short- or equal-styled,
probably the latter. These four plants were kept separate and allowed
to fertilize themselves; from their seed the seventeen plants in the
Table were raised, which proved all equal-styled. The stamens stood low
down in the corolla as in the long-styled form; and the stigmas, which
were globular and smooth, were either completely surrounded by the
anthers or stood close above them. My son, Mr. W. E. Darwin, made
magnified drawings for me, by the aid of the camera lucida, of the
pollen of one of the above equal-styled plants; and, in accordance with
the position of the stamens, the pollen resembled in the small size of
the grains that of the long-styled form. My son also examined pollen
from two equal-styled plants which he procured at Southampton,
and in both of these the grains differed extremely in size, a large
number being small and shrivelled, whilst many were fully as large as
those of the short-styled form and rather more globular. It is
possible, or even probable, that the increased size of the grains in
these plants was due, not to their having assumed the character of the
short-styled form, but to monstrosity; for Max Wichura observed
pollen-grains of monstrous size in certain hybrids. The vast number of
the small and shrivelled grains in the above two cases explains the
fact that though equal-styled plants are generally fertile in a high
degree, yet some yield few seeds. From the mutual position of the
stigma and anthers in the above seventeen plants they could hardly fail
to fertilize themselves; and accordingly four of them spontaneously
yielded no less than 180 capsules; of these the gardener selected eight
fine capsules for sowing; and they included on an average 54.8 seeds,
with a maximum of seventy-two. He gave me thirty other capsules, not
selected, of which twenty-seven contained good seeds, averaging 35.5
seeds, with a maximum of seventy; but if six poor capsules, each with
less than thirteen seeds, be excluded, the average rises to 42.5. These
are higher numbers than could be expected from either ordinary form
when self-fertilized, and accord with the view that the male organs
belong to one form, and the female organs partially to the other form;
so that a self-union with the equal-styled variety is in fact a
legitimate union.

Seed was saved from the above seventeen self-fertilized
equal-styled plants, and produced sixteen plants, which all proved
equal-styled, and resembled their parents in all the before-specified
respects. The stamens, however, in one plant were seated higher up in
the tube of the corolla than in the true long-styled form;

in another plant almost all the anthers were
contabescent. These sixteen plants were the grandchildren of the four
original plants, which probably were equal-styled; so that this
abnormal condition has been faithfully transmitted, probably, through
three, and certainly through two generations. The fertility of one of
these grandchildren was carefully observed: six flowers were fertilized
with pollen from the same flower, and produced six capsules, containing
on an average sixty-eight seeds, with a maximum of eighty-two and a
minimum of forty. Thirteen capsules spontaneously
self-fertilized yielded an average of 53.2 seeds, with the astonishing
maximum in one capsule of ninety-seven seeds, and a minimum of
fourteen, which latter capsule might fairly have been excluded, and
then the average would have been higher. In no legitimate union has so
high an average as sixty-eight seeds been observed by me, or nearly
such high maxima as eighty-two and ninety-seven. Hence these plants not
only have lost their proper dimorphic structure and peculiar functional
powers, but have acquired an abnormal grade of fertility—unless,
indeed, their high fertility may be accounted for by the stigmas
receiving pollen from the circumjacent anthers at exactly the most
favourable period.

With respect to Mr. Duck's lot in the Table, seed was
saved from a single plant, of which the form was not observed, and this
produced nine equal-styled and twenty long-styled plants. The
equal-styled resembled in all respects those previously described; and
eight of their capsules spontaneously self-fertilized contained on an
average 44.4 seeds, with a maximum of sixty-one and a minimum of
twenty-three. In regard to the twenty long-styled plants, the pistil in
some of the flowers did not project quite so high as in the ordinary
long-styled form; and the stigmas, though properly elongated, were
smooth; so that we have a slight approach in structure to the pistil of
the short-styled form. So it also is in function; for one of these
plants produced no less than fifteen spontaneously self-fertilized
capsules, and eight of these contained on an average 31.7 seeds, with a
maximum of sixty-one. This average would be rather low for a
long-styled plant artificially fertilized with its own pollen, but is
high for one spontaneously self-fertilized. For instance, thirty-four
capsules produced by the illegitimate grandchildren of a long-styled
plant, spontaneously self-fertilized, contained on an average only 9.1
seeds, with a maximum of forty-six. Some seeds indiscriminately saved
by the gardener from the foregoing equal-styled and long-styled plants
produced sixteen seedlings (grandchildren of the original single

plant belonging to Mr. Duck), which consisted of
fourteen equal-styled and two long-styled plants; and I mention this
fact as an additional instance of the transmission of the equal-styled
variety.

The third lot in the Table, namely the Baston plants,
are the last which need be mentioned. The long- and short-styled plants
were descended from a distinct stock from the fifteen equal-styled
plants. The latter were derived from a single plant, which the gardener
is positive was not long-styled; hence, probably, it was equal-styled.
In all these fifteen plants the anthers, occupying the same position as
in the long-styled form, closely surrounded the stigma, which in one
instance alone was slightly elongated. Notwithstanding this position of
the stigma, the flowers, as the gardener assured me, did not yield many
seeds; and this difference from the foregoing cases may perhaps have
been caused by the pollen being bad, as in some of the Southampton
equal-styled plants.

Conclusions with respect to the equal-styled
variety of P. sinensis.—That this is a variation, and not a
third or distinct form, as in the trimorphic genera Lythrum and
Oxalis, is clear; for we have seen in an illegitimate
long-styled plant its first appearance; and in the case of Mr. Duck's
seedlings, long-styled plants, only slightly deviating from the normal
state, and equal-styled plants were produced from the same
self-fertilized parent. The position of the stamens in their proper
place low down in the tube of the corolla, together with the small size
of the pollen-grains, show, first that the equal-styled variety is a
modification of the long-styled form, and secondly that the pistil is
the part which varies, as indeed was obvious in many of the plants.
This variation is of frequent occurrence, and when it has once appeared
is strongly inherited. It would have possessed little interest if is
had consisted of a mere change of structure; but this is accompanied by
modified fertility. Its occurrence apparently stands in close
relation with the illegitimate birth of the affected plant, and is
probably due to reversion; but to this point I shall recur at the close
of this paper.

PRIMULA AURICULA.

Although I made no experiments on the illegitimate
offspring of this species, I refer to it for two reasons:—First,
because I have observed two equal-styled plants in which the pistil
resembled in all respects that of the long-styled form,

whilst the stamens had become elongated as in the
short-styled form, so that the stigma was almost surrounded by the
anthers. The pollen-grains, however, of the elongated stamens resembled
in their small size those of the shorter stamens of the long-styled
form. Hence these plants have been rendered equal-styled by the
increased length of the stamens, instead of, as with P.sinensis,
by the diminished length of the pistil. Mr. J. Scott observed five
other plants in the same state, and he shows* that one of them, when
self-fertilized, yielded more seed than an ordinary long- or
short-styled form would have done when similarly fertilized, but that
it was far inferior in fertility to either form when legitimately
crossed. Hence it appears that the male and female organs in this
equal-styled variety were in a deteriorated condition, but had been
modified in some special manner so as mutually to act on each other
more efficiently than in the case of either of the ordinary forms.

The second point which deserves notice is that florists
always throw away the long-styled plants, and save seed exclusively
from the short-styled form. Nevertheless, as Mr. Scott was informed by
a man who raises this species extensively in Scotland, about one-fourth
of the seedlings appear long-styled; so that the short-styled form of
the Auricula, when fertilized by its own pollen, does not reproduce the
same form in so large a proportion as in the case of P. sinensis. We
may further infer that the short-styled form is not rendered quite
sterile by a long course of fertilization with pollen of the same form;
but as there would always be some liability to an occasional cross with
the other form, we cannot tell how long self-fertilization has been
continued. It is possible that our cultivated plants may be much more
sterile than those in a state of nature; for Grallesio† speaks with
surprise of the exuberant fertility in Italy of the Auricula when it is
crossed.

PRIMULA VULGARIS, Brit. Fl.

Var. acaulis of Linn., and P.acaulis
of Jacq.

Before giving my observations on the illegitimate
offspring of the Primrose, it will be convenient to show, under the
form of a Table, the degree of fertility in this species of the two
illegitimate and two legitimate unions; for this has not hitherto been
anywhere recorded:—

Var. rubra.—Mr. Scott states† that this
variety, which grew in the Botanic Garden in Edinburgh, was quite
sterile when fertilized by pollen from the common Primrose, as well as
from a white variety of the same species, but that some of the plants,
when artificially fertilized with their own pollen, yielded a moderate
supply of seed. He was so kind as to send me some of the
self-fertilized seed, from which I raised the plants immediately to be
described. I may premise that my experiments on the seedlings, made on
a large scale, do not accord in the result with those made by Mr. Scott
on the parent plant.

First, in regard to the transmission of form and
colour. The parent plant was long-styled, and of a rich purple colour.
From the self-fertilized seed 23 plants were raised; of these 18 were
purple, of different shades, with 2 of them a little streaked and
freckled with yellow, thus showing a tendency to reversion; and 5 were
yellow, but generally with a brighter orange centre than in the wild
flower. All the plants were profuse flowerers. All were long-styled;
but the pistil varied a good deal in length even on the same plant,
being rather shorter, or considerably longer, than in the normal
long-styled form; and the stigmas likewise varied in shape. Hence it is
probable that an equal-styled variety of the primrose would be found by
careful search; and I have received two accounts of plants apparently
in this condition. The stamens

in the seedlings always occupied their proper position
low down in the corolla; and the pollen-grains were of the small size
proper to the long-styled form, but were mingled with many minute and
shrivelled grains. The yellow-flowered and the purple-flowered plants
of this first generation were fertilized under a net by their own
pollen, and the seed separately sown. From the former, 22 plants were
raised, and all were yellow and long-styled. From the latter or the
purple-flowered plants, 24 long-styled plants were raised, of which 17
were purple and 7 yellow. In this last case we have an instance of
reversion in colour, without the possibility of any cross, to a
great-grandparent or to a more distant ancestor if the parent of the
Edinburgh plant was not yellow. Altogether, 23 plants in the first
generation, and 46 in the second generation, were raised; and the whole
of these 69 illegitimate plants were long-styled.

Eight purple-flowered and two yellow-flowered plants of
the first illegitimate generation were fertilized in various ways by
their own pollen and by that of the common Primrose; and the seeds were
separately counted, but I could detect no difference in the fertility
of the purple and yellow varieties. Hence, in the Table on the
following page, the results are run together.

If we compare the figures in this Table with those
previously given, showing the normal fertility of the common Primrose,
we shall see that the illegitimate purple- and yellow-flowered
varieties are very sterile. For instance, 72 flowers were fertilized
with pollen from the same plants and produced only 11 good capsules;
but by the standard they ought to have produced 48 capsules; and each
of these ought to have contained on an average 52.2 seeds, instead of
only 11.5 seeds. When these plants were illegitimately and legitimately
fertilized by pollen from the common Primrose, the average numbers were
increased, but were far from attaining the normal standards. So it was
when both forms of the common Primrose were fertilized by pollen from
the illegitimate varieties; and this shows that their male as well as
their female organs are in a deteriorated condition. The sterility of
these plants was shown in another way, namely, by their not producing
any capsules when the access of all insects (except such minute ones as
Thrips) was prevented; for under these circumstances the common
long-styled Primrose produces a considerable number of capsules. Hence
there can be no doubt that the fertility of these plants is greatly
impaired. The loss is not correlated with the colour of the flower; and
it was to ascertain this point that I made

so many experiments. As the parent plant growing in
Edinburgh was found by Mr. Scott to be in a high degree sterile, it may
have transmitted the same tendency to its offspring, independently of

Nature
of plant experimented on, and kind of union.

Number
of flowers fertilized.

Number
of good capsules.

Average
number of seeds per capsule.

Maximum
number of seeds in any one capsule.

Minimum
number of seeds in any one capsule.

Purple- and
yellow-flowered illegitimate long-styled plants, illegitimately fertilized
by pollen from the same plant...

72

11

11.5

26

5

Purple- and
yellow-flowered illegitimate long-styled plants, illegitimately fertilized
by pollen from the common long-styled primrose

72

39

31.4

62

3

Or, if the ten
poorest capsules, including less than 15 seeds,
be rejected, we get...

72

29

40.6

62

18

Purple- and
yellow-flowered illegitimate long-styled plants, legitimately fertilized
by pollen from the common short-styled Primrose...

26

18

36.4

60

9

Or, if the two
poorest capsules, including less than 15 seeds,
be rejected, we get...

26

16

41.2

60

15

The long-styled form
of common Primrose, illegitimately fertilized
by pollen from the long-styled illegitimate purple- and yellow-flowered
plants...

20

14

15.4

46

1

Or, if the three
poorest capsules be rejected, we get...

20

11

18.9

46

8

The short-styled
form of common Primrose, legitimately fertilized
by pollen from the long-styled illegitimate purple- and yellow-flowered
plants

10

6

30.5

61

6

their illegitimate birth. I am, however, inclined to
attribute some weight to the illegitimacy of their descent, both from
the analogy of other cases, and more especially from the fact that when
the plants were legitimately fertilized by pollen of the
common Primrose they yielded an average, as may be seen in the Table,
of only five more seeds than when illegitimately fertilized
by the same pollen. Now we know that it is eminently characteristic of
the

Seeds from the short-styled form of the Cowslip
fertilized by the same-form pollen germinate so badly that I raised
from three successive sowings only fourteen plants, which consisted of
nine short-styled and five long-styled plants. Hence the short-styled
form of the cowslip, when self-fertilized, does not transmit the same
form nearly so truly as does that of P. sinensis.From
the
long-styled form, fertilized by its own-form pollen, I first raised
three long-styled plants, and from their self-fertilized seed 53
long-styled grandchildren, from their seed 4 long-styled
great-grandchildren, and again from their seed 20 long-styled
great-great-grandchildren. From two other long-styled plants,
fertilized by their own-form pollen, 72 plants were raised, which
consisted of 68 long-styled and 4 short-styled. As in this latter case
the two parent plants, whilst under the net, did not produce a
sufficiency of pollen, I committed, through forgetfulness, a capital
error, and took some pollen from an adjoining uncovered long-styled
plant. Now I have found on the proboscis of humble-bees of two species
and of a moth (Cucullia), which were caught sucking the flowers of the
Cowslip, an abundance of pollen of both forms. Hence, by taking the
anthers of the uncovered long-styled plant, which probably had been
visited by insects, the flowers under the net might have accidentally
received a few grains from the short-styled form. Whether the
appearance of the four short-styled plants in this set of seedlings may
thus be accounted for I know not; but it is the sole exception which
has occurred with me of a long-styled form of any plant, when
self-fertilized, failing to produce the same form. Dr. Hildebrand,
however, states that, out of 17 plants of P. sinensis derived
from the self-fertilized long-styled form, three were short-styled.
Altogether, in the first lot of seedlings, consisting of four
generations, and in the second lot, 152 plants were raised, and all
were long-styled with the exception of the just-mentioned four
short-styled plants.

From the first seeds sown I raised from a
self-fertilized short-styled plant one short-styled and two long-styled
plants, and from a self-fertilized long-styled plant three long-styled
plants. The fertility of these six illegitimate plants was carefully
observed.

But I must here premise that I cannot give any accurate
standard of comparison as far as the number of the seeds is concerned;
for though I counted the seeds of many legitimate or ordinary plants
when fertilized in various ways, the number of seeds varied so greatly
during successive seasons that it would obviously have been unfair to
take a general average as the standard of comparison for illegitimate
unions made during any particular season. Moreover the seeds in the
same capsule frequently differ so much in size that it is scarcely
possible to decide which ought to be counted as good seed. There
remains as a standard of comparison the proportional number of
fertilized flowers which produce capsules containing any seed. Some of
the above six plants were so excessively sterile during successive
seasons, that no doubt could be entertained on the subject.

First, for the one illegitimate short-styled plant. In
the course of three seasons 27 flowers were illegitimately fertilized
by pollen from the same plant, and they yielded only a single capsule,
which contained a rather high number of seeds for a union of this
nature, namely, 23 seeds. As a standard of comparison I must add that
during the same three seasons 44 flowers borne by legitimate
short-styled plants were self-fertilized, and yielded 26 capsules; so
that the fact of the 27 flowers on the illegitimate plant having
produced only one capsule proves how sterile it was. To show that the
conditions of life were favourable, I should here state that numerous
plants of this and other species of Primula all produced an
abundance of capsules whilst growing in the same soil and situation as
the present and following plants. The sterility in the above
illegitimate short-styled plant depended on both the male and female
organs being in a deteriorated condition. This was manifestly the case
with the pollen; for many of the anthers were shrivelled or
contabescent. Nevertheless some of the anthers contained pollen, with
which I succeeded in fertilizing some flowers on the illegitimate
long-styled plants immediately to be described. Four flowers on this
same short-styled plant were likewise legitimately fertilized
with pollen from one of the following long-styled plants; but only one
capsule was produced, containing 26 seeds; and this is a very low
number for a legitimate union.

With respect to the five illegitimate long-styled
plants, derived from self-fertilized short-styled and long-styled
parents, their fertility was observed during the same three years.
These five plants, when self-fertilized, differed considerably from
each other

in fertility, as in the case of the illegitimate
long-styled plants of Lythrum Salicaria; and their fertility
varied much according to the season. I may premise, as a standard of
comparison, that during the same years 56 flowers on legitimate or
ordinary long-styled plants of the same age, and grown in the same
soil, were fertilized with their own pollen, and yielded 27 capsules.
On the first of the five illegitimate long-styled plants, 36 flowers
were self-fertilized in the course of the three years, but they did not
produce a single capsule. Many of the anthers on this plant were
contabescent; but some seemed to contain sound pollen: nor were the
female organs quite impotent; for I obtained from a legitimate cross
one capsule with good seed. On the second illegitimate long-styled
plant, 44 flowers were fertilized during the same years with their own
pollen, but they produced only a single capsule. The third and fourth
plants were in a very slight degree more productive. The fifth and last
plant was decidedly more fertile; for 42 self-fertilized flowers
yielded 11 capsules. Altogether, in the course of the three years, no
less than 160 flowers produced by the five illegitimate long-styled
plants were fertilized with their own pollen, and yielded only 22
capsules. According to the standard above given, they ought to have
produced 80 capsules. These 22 capsules contained on an average 15.1
seeds. I believe, subject to the doubts before specified, that with
legitimate plants the average from a union of this nature would have
been above 20 seeds. Twenty-four flowers on the same five illegitimate
plants were legitimately fertilized by pollen from the above-described
illegitimate short-styled plants, and produced only 9 capsules, which
is an extremely small number for a legitimate union. These 9 capsules,
however, contained an average of 38 apparently good seeds, which is as
large a number as legitimate plants sometimes yield. But this high
average was almost certainly false; and I mention the case for the sake
of showing the difficulty of arriving at a fair result; for this
average mainly depended on two capsules containing the extraordinary
numbers of 75 and 56 seeds; but these seeds, though I felt bound to
count them, were so poor that, judging from trials actually made in
other cases, I do not suppose that one would have germinated; and
therefore they ought not to have been included. Lastly, 20 flowers were
legitimately fertilized by pollen from a legitimate plant, and this
increased their fertility; for they produced 10 capsules. Yet this is
but a very small proportion for a legitimate union.

and the one short-styled illegitimate plant were
extremely sterile. Their sterility was shown, as in the case of
hybrids, in another way, namely, by their flowering profusely, and
especially by the long endurance of the flowers. For instance, I
fertilized many flowers on these plants, and fifteen days subsequently
(viz. on March 22nd) I fertilized numerous long-styled and short-styled
flowers on common Cowslips which grew close by. These latter
flowers, on April 8th, were withered, whilst most of the illegitimate
flowers remained quite fresh for several days subsequently; so that
some of these illegitimate plants, after being fertilized, remained in
full bloom for above a month.

I must add a few words on the degree of fertility of
the 53 illegitimate long-styled grandchildren, descended from the
long-styled plant which was first fertilized with its own pollen. The
pollen in two of these grandchildren was examined and found to include
a multitude of small and shrivelled grains. Nevertheless these plants
were not very sterile; for 25 flowers, fertilized with their own
pollen, produced 15 capsules, containing an average of 16.3 seeds. As
already stated, the probable average with legitimate plants for a union
of this nature is rather above 20 seeds. But it should be observed that
these plants were remarkably healthy and vigorous, being placed under
highly favourable conditions, and grown in pots in the greenhouse; and
we shall hereafter have occasion to show that such treatment greatly
increases the fertility of the Cowslip. When these same plants were
planted during the next year (which, however, was unfavourable) out of
doors, in the same place with all the other plants, 20 self-fertilized
flowers produced only 5 capsules, containing extremely few and wretched
seeds. Four long-styled great-grandchildren were raised, as previously
stated, from the self-fertilized grandchildren: they were kept under
the same highly favourable conditions in the greenhouse; and 10
self-fertilized flowers yielded the large proportion of 6 capsules,
containing on an average 18.7 seeds. Although, under the circumstances
just stated, we cannot compare the fertility of these plants with those
of the first generation, grown out of doors, yet we may infer that
illegitimate descent during three successive generations did not much,
or at all, increase their sterility.

Equal-styled red variety of P. veris.—Mr.
Scott has described* a plant of this kind growing in the Botanic
Garden of Edinburgh. He states that it was highly self-fertile,
although insects were

excluded; and he explains this anomalous circumstance
by showing, first, that the anthers and stigma are in close apposition,
and, secondly, that the stamens with their pollen resemble the stamens
of the short-styled form, whilst the pistil resembles that of the
long-styled form both in length and in the structure of the stigma.
Hence the self-union of this variety is, in fact, a legitimate union,
and consequently is highly fertile. Mr. Scott further states that this
variety yielded very few seeds when fertilized by either the long- or
short-styled common Cowslip, and, again, that both forms of the latter,
when fertilized by the equal-styled variety, likewise produced very few
seeds. But the experiments with the Cowslip tried by Mr. Scott were few
in number; and I suspect that the results were accidental. Anyhow my
observations on equal-styled seedlings derived from the Edinburgh plant
do not, as we shall see, confirm his results.

I raised 20 plants from self-fertilized seed sent me by
Mr. Scott; and they all produced red flowers, varying slightly in tint.
Of these, two were strictly long-styled both in structure and in
function; for their reproductive powers were tested by crosses with
both forms of the common cowslip. Six plants were equal-styled; but on
the same plant the pistil varied a good deal in length during different
seasons. This was likewise the case, according to Mr. Scott, with the
parent plant. Lastly, 12 plants were in appearance short-styled; but
they varied much more in the length of their pistils than the ordinary
short-styled Cowslip, and they differed widely from the latter in their
powers of reproduction. Short-styled Cowslips, when insects are
excluded, are extremely barren: for instance, on one occasion six fine
plants produced only about 50 seeds (that is, less than the product of
two good capsules), and on another occasion not a single capsule. Now,
when the above 12 so-called short-styled seedlings were similarly
treated, all, except two or three, produced a great abundance of
capsules, containing numerous seeds, which germinated remarkably well.
Moreover three of these plants, which during the first year were
furnished with quite short pistils, on the following year produced
pistils of extraordinary length. Hence the greater number of the
so-called short-styled plants cannot be distinguished in function from
the equal-styled variety, which they likewise partially resemble in
structure. The stamens in all these eighteen plants are seated high up
in the corolla, as in the true short-styled Cowslip; and the
pollen-grains resemble those of the same form in their large size, but
are mingled with a few shrivelled grains. In function

this pollen is identical with that of the short-styled
Cowslip; for ten long-styled flowers of the common Cowslip were
legitimately fertilized by pollen from a true equal-styled variety, and
produced six capsules, containing on an average 34.4 seeds; whilst
seven capsules on a short styled Cowslip illegitimately fertilized by
the same pollen yielded an average of only 14.5 seeds.

As the eighteen equal-styled and so-called short-styled
plants differ from each other in their powers of reproduction, and as
this is an important subject, I will give a few details with respect to
five of them. First, an equal-styled plant, protected from insects (as
in all the following cases, with one stated exception), spontaneously
produced numerous capsules, five of which gave an average of 44.8
seeds, with a maximum in one capsule of 57. But six capsules, which had
been fertilized by pollen from a short-styled Cowslip (and this is a
legitimate union), gave an average of 28.5 seeds, with a maximum of 49;
and this is a much lower average than might have been expected.
Secondly, nine capsules from an equal-styled plant, which was not protected
from insects, but probably was self-fertilized, gave an average of 45.2
seeds, with a maximum of 58. Thirdly, a plant which had a very short
pistil in 1865, produced spontaneously many capsules, six of which
contained an average of 33.9 seeds, with a maximum of 38. In 1866 this
same plant had a pistil of wonderful length; for it projected quite
above the anthers, and the stigma resembled that of the long-styled
form. In this condition it produced spontaneously a vast number of fine
capsules, six of which contained almost exactly the same average number
as before, viz. 34.3, with a maximum of 38. Four flowers on this plant,
legitimately fertilized by pollen from a short-styled cowslip, yielded
capsules with an average of 30.2 seeds. Fourthly, a short-styled plant
spontaneously produced in 1865 an abundance of capsules, ten of which
contained an average of 35.6 seeds, with a maximum of 54. In 1866 it
had become in all respects long-styled, and ten capsules gave almost
exactly the same average, viz. 35.1 seeds, with a maximum of 47. Eight
flowers on this plant, legitimately fertilized by pollen from a
short-styled Cowslip, produced six capsules, with the high average of
53 seeds, and the high maximum of 67. Eight flowers were also
fertilized by pollen from a long-styled Cowslip (this being an
illegitimate union), and produced seven capsules, containing an average
of 24.4 seeds, with a maximum of 32. The fifth and last plant remained
in the same condition during both years: it had a pistil rather longer
than that of the true short-styled form,

with the stigma smooth, as it ought to be in this form,
but abnormal in shape, like a much-elongated inverted cone. It produced
spontaneously many capsules, five of which, in 1865, gave an average of
only 15.6 seeds; and in 1866 ten capsules still gave an average only a
little higher, viz. of 22.1, with a maximum of 30. Sixteen flowers were
fertilized by pollen from a long-styled Cowslip, and produced 12
capsules, with an average of 24.9 seeds and a maximum of 42. Eight
flowers were fertilized by pollen from a short-styled Cowslip, but
yielded only two capsules, containing 18 and 23 seeds. Hence this
plant, in function and partially in structure, is in an almost exactly
intermediate state between the long-styled and short-styled form, but
inclining towards the short-styled; and this accounts for the low
average of seeds which it produced when spontaneously self-fertilized.

We thus see that the foregoing five plants differ much
from each other in fertility. In two individuals a great
difference in the length of the pistil during two succeeding years made
no difference in the number of seeds produced. As all five plants
possessed the male organs of the short-styled form in a perfect state,
and the female organs of the long-styled form in a more or less
complete state, they spontaneously produced a surprising number of
capsules, which generally contained a large average of remarkably good
seeds. With ordinary Cowslips, legitimately fertilized, I once
obtained from plants cultivated in the greenhouse the high average,
from seven capsules, of 58.7 seeds, with a maximum in one capsule of 87
seeds; but from plants grown out of doors I never obtained a higher
average than 41 seeds. Now two of the equal-styled plants, grown out of
doors and spontaneously self-fertilized, gave averages of 44 and 45
seeds; but this high fertility may perhaps be attributed to the stigma
receiving pollen from the surrounding anthers at exactly the right
period. Two of these plants, fertilized by pollen from the long-styled
cowslip (and this in fact is a legitimate union), gave a lower average
than when self-fertilized. On the other hand, one plant, when similarly
fertilized by the Cowslip, yielded the unusually high average of 53
seeds, with a maximum of 67. Lastly, as we have just seen, one of these
plants was in an almost exactly intermediate condition in its female
organs between the long- and short-styled forms, and consequently, when
self-fertilized, yielded a low average of seed. If we add together all
the experiments which I made on the equal-styled plants, 41
spontaneously self-fertilized capsules (insects having been excluded)
gave an average of 34 seeds, which is exactly the same

number as the parent plant yielded in Edinburgh.
Thirty-four flowers, fertilized with pollen from the long-styled
Cowslip (and this is an analogous union), produced 17 capsules,
containing an average of 33.8 seeds. It is a rather singular
circumstance, for which I cannot account, that 20 flowers, artificially
fertilized with pollen from the same plants, yielded only ten capsules,
containing the low average of 26.7 seeds.

As bearing on inheritance, it may be added that 72
seedlings were raised from one of the red-flowered strictly
equal-styled self-fertilized plants derived from the Edinburgh plant
which was similarly characterized. These 72 grandchildren all bore, as
in the first generation, red flowers, with the exception of one plant,
which reverted in colour to the common Cowslip. In regard to structure,
nine plants were truly long-styled, and had their stamens seated low
down in the corolla in the proper position; the remaining 63 plants
were equal-styled, though the stigma in about a dozen of them stood a
little below the anthers. We thus see that the anomalous combination in
the same plant, of male and female sexual organs which properly exist
in distinct forms or plants, is inherited with much force. Thirty-six
seedlings were also raised from long- and short-styled common Cowslips,
crossed by pollen of the equal-styled variety. Of these
plants one alone was equal-styled, 20 were short-styled but with the
pistil in three of them rather too long, and the remaining 15 were
long-styled. In this case we have an illustration of the difference
between simple inheritance and prepotency of transmission; for the
equal-styled variety, when self-fertilized, transmits its character, as
we have seen, with much force, but when crossed with the common Cowslip
cannot withstand the greater power of transmission of the latter.

Genus PULMONARIA.

I have little to say on this genus. I obtained some
seeds of P. officinalis from a garden where the long-styled
form alone grew, and raised eleven seedlings, which were all
long-styled. These plants were named for me by Dr. Hooker; but I have
some doubts whether they belong to the same species as that described
under the same name by Dr. Hildebrand*; for he found the long-styled
form absolutely sterile with its own pollen, whilst my long-styled
seedlings and the parent plants when self-fertilized yielded a fair
supply of seed. It is, however, possible that these plants may have
varied in function, as in the case of the so-called short-

styled individuals belonging to the equal-styled
variety of Primula veris, and thus have become self-fertile.
The long-styled form of Pulmonaria angustifolia is, like Dr.
Hildebrand's plant, absolutely sterile with its own pollen, so that I
could never procure a single seed. On the other hand, the short-styled
form, differently from that of P. officinalis, is fertile
with its own pollen in a quite remarkable degree for a dimorphic plant.
From seeds carefully self-fertilized I raised 18 plants, of which 13
proved to be short-styled and 5 long-styled. I did not observe their
power of producing seed; but this, from the fertility of the first
union, probably would have been nearly perfect.

CONCLUSIONS IN REGARD TO THE ILLEGITIMATE OFFSPRING
OF TRIMORPHIC AND DIMORPHIC PLANTS.

It is remarkable in how many points and how closely
illegitimate unions between the two or three forms of the same species,
together with their illegitimate offspring, resemble hybrid unions
between distinct species together with their hybrid offspring. In both
cases we meet with every degree of sterility, from very slightly
lessened fertility to absolute barrenness, when not even a single
seed-capsule is produced. In both cases the facility of effecting the
first union is much influenced by the conditions to which the plants
are exposed*. Both with hybrids and illegitimate plants the innate
degree of sterility is highly variable in plants raised from the same
mother plant. In both cases the male organs are more plainly affected
than the female; and we often find contabescent anthers enclosing
shrivelled and utterly powerless pollen-grains. The more sterile
hybrids, as Max Wichura has well shown, are sometimes much dwarfed in
stature, and have so weak a constitution that they are liable to
premature death; and we have seen exactly parallel cases with the
illegitimate seedlings of Lythrum and Primula. Many
hybrids are the most persistent and profuse flowerers, as are some
illegitimate plants. When a hybrid is crossed by either pure parent
form, it is notoriously much more fertile than when crossed inter
se or by another hybrid; so when an illegitimate plant is
fertilized by a legitimate plant, it is more fertile than when
fertilized inter se or by another illegitimate plant. When
two species are crossed and they produce numerous

* This has been remarked by
many experimentalists in effecting crosses between distinct species;
and in regard to illegitimate unions I have given a striking
illustration in the case of Primula veris in a foot-note to
my paper on Lythrum, in Proc Linn. Soc. vol. viii. (1864) p.
180.

seeds, we expect as a general rule that their hybrid
offspring will be moderately fertile; but if the parent plants produce
extremely few seeds, we expect that the hybrids will be very sterile.
But there are marked exceptions, as shown by Gärtner, to this rule. So
it is with illegitimate unions and illegitimate offspring: thus the
mid-styled form of Lythrum Salicaria, when illegitimately
fertilized by pollen from the longer stamens of the short-styled form,
produced an unusual number of seeds; and their illegitimate offspring
were not at all, or hardly at all, sterile. On the other hand, the
illegitimate offspring from the long-styled form, fertilized by pollen
from the same form, yielded few seeds, and the illegitimate offspring
thus produced were very sterile; but they were more sterile than might
have been expected relatively to the difficulty of effecting the union
of the parent sexual elements. No point is more remarkable in regard to
the crossing of species than their unequal reciprocity. Thus
species A will fertilize B with the greatest ease; but B will not
fertilize A after hundreds of trials. We have exactly the same case
with illegitimate unions; for the mid-styled Lythrum salicaria was
easily fertilized by illegitimate pollen from the longer stamens of the
short-styled form, and yielded many seeds; but the latter form did not
yield a single seed when fertilized by the longer stamens of the
mid-styled form.

Another important point is prepotency. Gärtner
has shown that when two species are fertilized with each other's
pollen, if they be afterwards fertilized with their own pollen, or with
that of the same species, this is so prepotent over the foreign pollen
that the effect of the latter, though placed on the stigma some time
previously, is entirely destroyed. Exactly the same thing occurs with
illegitimate unions, as I ascertained in the following manner: I
fertilized illegitimately a long-styled common Cowslip with pollen from
the same form, and exactly twenty-four hours afterwards I fertilized
the same stigmas legitimately with pollen from a short-styled dark-red
Polyanthus. I should state that I raised many seedlings from crossed
Cowslips and the Polyanthus, and know their peculiar appearance. I
further know by the test of the fertility of the mongrels, as well inter
se as with both parent forms, that the Polyanthus is a variety of
the Cowslip, and not of the Primrose (P. vulgaris) as
some authors have supposed. Now from the long-styled Cowslip,
fertilized in the manner just described, I raised thirty seedlings,
every one of which had flowers coloured more or less red, so that the
legitimate Polyanthus-pollen wholly obliterated the influence of the
illegitimate Cowslip-pollen

which had been placed on the stigmas twenty-four hours
previously, and not a single pure Cowslip was produced. We thus see
that there is the closest agreement in all the above-specified and most
characteristic points between hybrid unions with their hybrid offspring
and illegitimate unions with their illegitimate offspring.

The
parallelism in the two following relations is not so clear, but
apparently holds good. We know that when dimorphic and trimorphic
plants are legitimately fertilized the seedlings consist in about equal
numbers of the two or three proper forms. But we have seen that when
the long-styled Lythrum was illegitimately fertilized by its
own-form pollen, all the offspring, fifty-six in number, were
long-styled; so it was with the fifty-two illegitimate children and
grand-children of the long-styled Primula sinensis; with the
sixty-nine of P. vulgaris, and, with the exception of four
short-styled plants, with the 152 illegitimate children,
grandchildren, great-grandchildren, and great-great-grandchildren of
P. veris. The exceptional case of the four short-styled plants
may perhaps be accounted for by an error, as previously explained, in
the method of fertilization. Lastly, from the self-fertilized
long-styled Pulmonaria officinalis eleven seedlings were
raised, and these were all long-styled. Dr. Hildebrand has recorded an
analogous case with the long-styled form of Oxalis rosea. With
respect to the short-styled form, when plants of this nature are
illegitimately fertilized by their own-form pollen, short-styled
offspring are generally produced in unnaturally large proportion*. In
two instances when one form of the Lythrum was
illegitimately fertilized, not by its own-form pollen, but by that of
another form, the offspring (thirty-seven in number) belonged to thetwo parent forms, but not one to the third form, as would have
occurred with a legitimate union. From a third illegitimate union
between the forms of Lythrum the offspring (forty in number)
consisted of all three forms in rather unequal proportions; but this
union was much less sterile than any other illegitimate union. From
these various facts it is manifest that an illegitimate union seriously
disturbs the natural and proper proportional numbers of the two or
three sexual forms. Now if we turn to hybrid unions between species
which have their

* Since this paper was read before the
Society, I have raised illegitimate seedlings from both the long-styled
and short-styled forms of Polygonum Fagopyrum or common
Buckwheat. As yet only 49 seedlings from the self-fertilized
long-styled form have flowered, and of these 45 are long-styled and
four short-styled; so that the rule does not here hold quite so
strictly as in the cases given in the text. Of the 33 seedlings from
the self-fertilised short-styled form, 19 are short-styled and 14 are
long-styled.

sexes separated, we find something of the same kind;
for Max Wichura* has shown that with hybrid willows the proportion
between the male and female plants is very different from what it is
with the pure parent species. Naudin† has also observed in the case of
hybrid Luffæ that the racemes, which ought to bear
male
flowers alone, included both sexes, and that some plants had become
female by the complete disappearance of the male flowers. With hybrid
animals the just proportion of the two sexes is likewise disturbed, the
males being in excess‡. Hence hybridism, like illegitimacy of birth,
certainly appears to affect the sex of the offspring.

It is manifest,
from the facts previously given, that there is a strong tendency in Primula
sinensis, veris, Auricula, and vulgaris to
produce
equal-styled varieties. This singular variation may be compared with
those cases of monstrous hermaphroditism which occasionally occur both
in the animal and vegetable kingdoms; for as with unisexual organisms
the opposite sexes are sometimes combined in the same individual in a
more or less perfect manner, so here the opposite or reciprocal sexual
forms are combined in the same plant and flower. In Primula
sinensis, vulgaris, and veris it is the
female organ or
pistil which varies; for the pistil in the first two species is
properly long-styled, and in the latter species properly short styled;
whilst in the long-styled P. Auricula it is the male organs
or stamens which vary. Illegitimate birth seems to be one
chief exciting cause of this variation; for I observed its first
appearance and various stages in illegitimate plants of P. sinensis;
and we know that it frequently occurs in P. Auricula, which
is generally propagated in an illegitimate manner. Simple cultivation,
however, suffices to cause it; for I observed one incipient case in a
long-styled P. veris which had been removed from the fields
and cultivated in good soil; and I have heard of instances in
cultivated long-styled plants of P. vulgaris. When this
variation

* Die Bastardbefruchtung im
Pflanzenreich, 1865, p. 43.

† Nouvelles Archives du Muséum, tom. i.
p. 113.

‡ This was first observed by Buffon, and
has since been confirmed, but perhaps hardly by sufficient facts, by
Flourens in his 'Longévité Humaine,' 1855, p. 154. Dr. O. Staudinger,
of Dresden, has recently informed me that he has never seen, in the
case of Lepidoptera, a single hybrid of the female sex. He has either
bred or obtained above sixty hybrids between Smerinthus ocellata ♂
and populi ♀; and all these are males except two, which are
partially hermaphrodites. This latter circumstance deserves notice in
reference to the subject discussed in the following paragraph of the
text, namely, on the tendency in illegitimate plants to combine both
sexual forms in the same plant; for this may be considered a kind of
hermaphroditism.

has once appeared, it is inherited with remarkable
force. Plants which have become equal-styled, and have thus lost their
dimorphic structure, are perfectly self-fertile, being quite as fertile
as ordinary plants when legitimately crossed. This being the case, and
as the variation so often arises, it may be asked why has it not
occurred under nature and been naturally selected or preserved. The
answer, no doubt, is that such plants would be eminently liable to
long-continued self-fertilization, which certainly entails a weak
constitution*.

As the great majority of plants of all kinds and even
some species of Primula† are non-dimorphic, the loss of
dimorphism in the equal-styled varieties may be attributed, as Mr.
Scott has remarked, to reversion to the primordial condition of the
plant; and this explains the force with which this modification is
inherited. We have also seen in illegitimate plants descended from the
long-styled P. sinensis that which appears to be another
case of reversion, namely, the small size and wild aspect of their
flowers. Now I have elsewhere‡ given abundant evidence showing that
the offspring of crossed species and varieties are eminently liable to
reversion. Hence in the cases in which illegitimate birth appears to
have been the exciting cause of reversion, illegitimacy has acted like
hybridization. The parallelism in this particular instance is close; in
a future paper I shall show that the common Oxlip is a
hybrid between P. veris and vulgaris; and I have
seen short-styled wild Oxlips which had become strictly equal-styled,
and others which exhibited gradations in the length of the pistil, but
not in the roughness of the stigma, leading to this same state, like
the gradations described under P. sinensis and veris.

Although there may be some doubt with respect to the
parallelism between illegitimate unions with their illegitimate
offspring and hybrid unions with their hybrid offspring, in regard to
the last two subjects discussed, namely, the disturbed proportions of
the sexual forms and sexes, and the appearance through reversion of
equal-styled varieties, there can be no doubt that the parallelism is
so close as to amount almost to identity in the following chief
characteristic points, namely:—the various grades of lessened
fertility up to complete barrenness—the fertility innately differ-

* See my work on the 'Variation of
Animals and Plants under Domestication,' 1868, vol. ii. chap. xvii.,
and especially p. 128.

ing in seedlings of the same parentage, and being much
affected by the nature of the conditions; the more sterile plants being
dwarfed in stature, weakly in constitution, and liable to premature
death; the anthers being often contabescent; the first unions and the
offspring being generally sterile in a parallel degree, but with marked
exceptions to the rule; the fertility of the offspring being increased
by a cross with a legitimate form, or with one of the pure parent
forms; the unequal reciprocity in sexual power between the same two
forms or between the same two species; and, lastly, the prepotent
action of legitimate pollen in the one case, and of the plant's own
pollen in the other case. Hence it is hardly an exaggeration to assert
that the illegitimate offspring from an illegitimate union are hybrids
formed within the limits of one and the same species.

This conclusion is important; for, as I have elsewhere*
more fully explained, we thus learn, first, that the lessened fertility
of the first union and of the offspring of two forms is no sure
criterion of specific distinctness. If any one were to cross two
varieties of the same form of Lythrum or Primula for
the sake of ascertaining whether they were specifically distinct, and
he found that they and their offspring were extremely sterile, and that
they resembled in a whole series of relations crossed species and their
hybrid offspring, he would maintain that his varieties had been proved
to be good and true species; but he would be completely deceived. In
the second place, as the forms of the same trimorphic or dimorphic
species are obviously identical, with the exception of the reproductive
organs, in general structure, and as they are identical in general
constitution (for they live under precisely the same conditions), the
sterility of their illegitimate unions, and that of their illegitimate
offspring, must depend exclusively on the nature of the sexual elements
and on their incompatibility for uniting in a particular manner. And as
we have just seen that distinct species when crossed resemble in a
whole series of relations the forms of the same species when
illegitimately united, we are led to conclude that in this case
likewise the sterility depends exclusively on the incompatible nature
of their sexual elements, and not on any general difference in
constitution or structure. We are, indeed, led to this same conclusion
by the impossibility of detecting any difference sufficient to account
for certain species crossing with the greatest ease, whilst other
closely

allied species cannot be crossed, or can only be
crossed with the greatest difficulty. We are led to this conclusion
still more forcibly by considering the great difference which often
exists in the facility of crossing reciprocally the same two species;
for it is clear in this case that the result must depend on the nature
of the sexual elements, the male element of the one species acting
freely on the female element of the other, but not so in the reversed
direction. And now we see that this same conclusion is independently
and strongly fortified by considering the illegitimate unions and
offspring of trimorphic and dimorphic plants. In so complex and obscure
a subject as hybridism it is no slight gain to arrive at a definite
conclusion, namely, that we must look exclusively to a functional
difference in the sexual elements, as the cause of the sterility of
species when first crossed, and of their hybrid offspring. It was this
consideration which led me to make so many and such laborious
observations as have been recorded in this paper, and which justify, I
think, their publication.